1. Field of the Invention
The present invention relates to a selective gas separator, and more particularly to a selective gas separator useful particularly for the separation of carbon monoxide.
2. Description of the Prior Art
For the preparation of a feed gas for chemical syntheses, it is an important technical subject to concentrate carbon monoxide from e.g. a gas obtained by the steam reforming or partial oxidation of hydrocarbons such as natural gas, light naphtha or heavy oil, or from a by-product gas from an iron-making process.
As a process for separating and concentrating carbon monoxide from a gas mixture containing carbon monoxide, there has been known an absorption method in which carbon monoxide is absorbed in an aqueous ammonium cuprous salt solution or an aqueous hydrochloric acid cuprous salt solution, or in a toluene solution of aluminum copper (I) chloride known as COSORB method, or a low temperature processing which is fundamentally different from the absorption method. However, these methods have problems such that heating is required for the release of carbon monoxide, the apparatus is expensive, or the operation cost is high.
Various polymer membranes have been known as membranes useful for the separation of gases from a gas mixture. However, the gas permeability constant of such membranes is relatively small, and a material having a higher permeability constant is desired. In the case where the membrane is liquid, it is usually possible to obtain a high permeability constant since the solubility constant and diffusion constant of a gas are thereby great. Further, if such a liquid membrane contains a substance which exhibits a reversible interaction selectively with a certain gas, it is possible to further increase the permeability of that gas. On the other hand, the selectivity of the membrane is attributable to the difference, among the gases, in the solubility in the membrane and the difference, among the gases, in the diffusion rate in the membrane. Accordingly, when the membrane contains a substance which exhibits a reversible interaction selectively with a particular gas, as mentioned above, the solubility of that gas can exclusively be increased, whereby the selectivity can remarkably be increased.
For the use of such a membrane containing a substance which exhibits a reversible interaction selectively with a certain gas, there have been known many instances, for example, the separation of carbon dioxide by means of an aqueous solution of an alkali metal bicarbonate (Japanese Examined Patent Publication No. 1176/1970), the separation of an olefin by means of an aqueous solution of silver nitrate (Japanese Examined Patent Publication No. 31842/1978), and the separation of nitrogen monoxide by means of a formamide solution of ferrous chloride (A.I Ch E Journal, vol 16, No. 3, p 405, 1970). These liquid membranes are used as being supported on a support. Further, with respect to the separation of carbon monoxide, it is known to use an aqueous hydrochloric acid solution of copper chloride. However, in this case, there is a drawback that a highly concentrated aqueous hydrochloric acid solution must be used. Furthermore, in the case where the secondary side (i.e. the outlet side) of the permeation is to be maintained under reduced pressure, there will be a difficulty that steam or hydrogen chloride gas permeates and mixes with other gas.